An aquabooster usually still has a coil in the boiler that gets domestic water in the booster tank circulated around by a bronze pump, so the boiler has to be kept up to at least 120° as to not suck the heat back out of the booster tank. An indirect keeps the domestic water in a tank but pumps hot boiler water through a coil in the tank to heat the water. A booter tank is cheaper but the bronze pump is expensive. If your tankless coil is old, it might need replacing also. Better to get rid of coil and just get an indirect.

The high efficency water heaters are good, but if they only last 10 years, they might not be worth the extra cost. A good stainless steel indirect should last 20 years.